Who is Participating?

You have to domain active directory servers. When you create a user account, that account is saved within active directory. The active directory database is shared with all other AD servers on the domain by default. So, you are talking about Active Directory Replication, and this is how that works:http://technet.microsoft.com/en-us/library/cc755994%28v=ws.10%29.aspx

You can take advantage of the Distributive File System Replication (DFSR). You can create a namespace and use DFSR for that namespace.

There are other means to "synch" with servers.. But, within a windows domain, DFSR and a Namespace is the most common. (it's also a built in feature).

Remember, you are not synchronizing. Instead, you are replicating data from one to the other. Under certain circumstances, the replication can seize or be delayed. So, you have to monitor your DFSR event logs, and also make sure you monitor your FRS (File Replication Service) event logs.

those two server are in domain master with a additional domain or watever the configuration is ... when u setup one server the master domain and u put a second server on the same florest this ll be per default the sync whoever you can change the time for the sync